Internal combustion engines generate exhaust as a by-product of fuel combustion within the engines. Engine exhaust contains, among other things, unburnt fuel, particulate matter such as soot, and gases such as carbon monoxide and NOx. To comply with regulatory emissions control requirements, it is desirable to reduce the amount of unburnt fuel, soot, and other gases in the engine exhaust. Due to the rising cost of liquid fuel (e.g. diesel fuel) and to comply with the emissions control requirements, engine manufacturers have developed dual-fuel engines and/or gaseous-fuel engines.
In these engines, using a lower-cost fuel, for example, a gaseous fuel together with or without liquid fuel helps improve the cost efficiency of the engine. Use of gaseous fuel to fully or partially replace the traditional liquid fuels such as, gasoline or diesel fuel, may also help to lower the amount of soot and/or other undesirable gases in the exhaust. To comply with increasingly stringent emissions control regulations, these engines may be operated with a lean air-fuel ratio, which may prevent the fuel from being fully burned within the combustion chamber.
Incomplete combustion of the fuel may result in the formation of undesirable amounts of NOx. Further, any fuel that remains unburnt and escapes from the combustion chambers does not participate in combustion, reducing the thermal efficiency of the engine. The escaping unburnt fuel also contributes to the total amount of undesirable emissions produced by the engine. Although the unburnt fuel and NOx may be removed from the exhaust in one or more after-treatment devices, implementing these devices adds to the cost of operating the engine. Therefore, it is desirable to reduce the amount of unburnt fuel and NOx in the exhaust leaving the combustion chamber.
One technique for improving combustion of the fuel in the combustion chamber is disclosed in U.S. Patent Application Publication No. 2014/0090621 A1 to Hernandez et al. (“the '621 publication”) that published on Apr. 3, 2014. The '621 publication discloses a combustion system that may be employed in an engine. The combustion system of the '621 publication includes a combustion chamber having one or more fuel injectors configured to spray fuel into the combustion chamber. The '621 publication discloses that the combustion chamber may include electrodes that can apply an electric field between the fuel injector and the combustion chamber. The '621 publication explains that fuel droplets exiting the fuel injectors may be charged and may follow a trajectory governed by the electric field established within the combustion chamber. The '621 publication discloses that all the fuel droplets have a substantially similar potential, which may cause them to repel each other and spread towards the combustion chamber head, combustion chamber sidewalls, and combustion chamber bottom.
Although the '621 publication discloses the use of an electric field to improve distribution of fuel droplets in a combustion chamber, the disclosed system may still be less than optimal. In particular, the method of the '621 publication does not control the amount of charge on the fuel droplets injected into the combustion chamber. Because fuel droplets having the same amount of charge may repel each other by a same distance, the distribution of fuel droplets within the combustion chamber may be suboptimal. Furthermore, the system of the '621 publication establishes an electric field between the fuel injectors and the combustion chamber walls. Thus, although the fuel droplets may repel each other, they may be attracted to the combustion chamber walls allowing the fuel droplets to impinge upon and stick to the combustion chamber walls. Fuel on the combustion chamber walls may not be fully burned during the combustion cycle and may be discharged with the exhaust exiting the combustion chamber.
The engine system of the present disclosure solves one or more of the problems set forth above and/or other problems in the art.